phase 2: mattes/migrate -> migratex (#848)

* move mattes migrations to migratex

* changes format of migrations to migratex format
* updates test runner to use new interface (double checked this with printlns,
the tests go fully down and then up, and work on pg/mysql)

* remove mattes/migrate

* update tests from deps

* update readme

* fix other file extensions

test/fn-api-tests/exec_test.go

@@ -360,9 +360,10 @@ func TestOversizedLog(t *testing.T) {
 	if err != nil {
 		t.Error(err.Error())
 	} else {
-		if len(logObj.Payload) >= size {
+		log := logObj.Payload.Log.Log
+		if len(log) >= size {
 			t.Errorf("Log entry suppose to be truncated up to expected size %v, got %v",
-				size/1024, len(logObj.Payload))
+				size/1024, len(log))
 		}
 	}
 	DeleteApp(t, s.Context, s.Client, s.AppName)